fix(editor): map .cts/.mts to the typescript language id (#11294)

* fix(editor): map .cts/.mts to the typescript language id

The comment above EXT_TO_LANGUAGE already documents that Monaco maps
.tsx/.cts/.mts onto the typescript language id, but only .tsx was in the
table, so .cts/.mts files opened as plaintext.

* fix(mobile): map cts and mts to typescript

---------

Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>

mobile/src/session/mobile-file-language.ts

@@ -10,6 +10,8 @@ function extname(filePath: string): string {
 const EXT_TO_LANGUAGE: Record<string, string> = {
   '.ts': 'typescript',
   '.tsx': 'typescript',
+  '.cts': 'typescript',
+  '.mts': 'typescript',
   '.js': 'javascript',
   '.jsx': 'javascript',
   '.mjs': 'javascript',

mobile/src/session/mobile-file-syntax.test.ts

@@ -11,9 +11,12 @@ import type { MobileDiffLine } from './mobile-diff-lines'
 describe('mobile file syntax highlighting', () => {
   it('detects common source languages from file paths', () => {
     expect(detectMobileFileLanguage('src/App.tsx')).toBe('typescript')
+    expect(detectMobileFileLanguage('config/vitest.config.mts')).toBe('typescript')
+    expect(detectMobileFileLanguage('C:\\repo\\scripts\\postinstall.CTS')).toBe('typescript')
     expect(detectMobileFileLanguage('scripts/deploy.sh')).toBe('shell')
     expect(detectMobileFileLanguage('Dockerfile')).toBe('dockerfile')
     expect(resolveMobileSyntaxLanguage('src/App.tsx')).toBe('typescript')
+    expect(resolveMobileSyntaxLanguage('worktrees/feature/build.cts')).toBe('typescript')
     expect(resolveMobileSyntaxLanguage('Dockerfile')).toBe('plaintext')
   })
 

src/renderer/src/lib/language-detect.test.ts

@@ -47,6 +47,18 @@ describe('detectLanguage', () => {
     expect(detectLanguage('C:\\Users\\alice\\.codex\\LOG.JSONL')).toBe('jsonl')
   })
 
+  it('maps .cts/.mts files to the Monaco built-in typescript language id (case-insensitive)', () => {
+    expect(detectLanguage('config/vitest.config.mts')).toBe('typescript')
+    expect(detectLanguage('scripts/postinstall.cts')).toBe('typescript')
+    expect(detectLanguage('types/global.d.mts')).toBe('typescript')
+    expect(detectLanguage('C:\\repo\\config\\BUILD.MTS')).toBe('typescript')
+  })
+
+  it('keeps .mjs/.cjs on the Monaco built-in javascript language id', () => {
+    expect(detectLanguage('scripts/build.mjs')).toBe('javascript')
+    expect(detectLanguage('scripts/legacy.cjs')).toBe('javascript')
+  })
+
   it('keeps .json/.jsonc on the built-in json language and unknown on plaintext', () => {
     expect(detectLanguage('config/settings.json')).toBe('json')
     expect(detectLanguage('config/tsconfig.jsonc')).toBe('json')

src/renderer/src/lib/language-detect.ts

@@ -14,6 +14,8 @@ const EXT_TO_LANGUAGE: Record<string, string> = {
   // is what gives .tsx/.jsx files syntax highlighting in the editor.
   '.ts': 'typescript',
   '.tsx': 'typescript',
+  '.cts': 'typescript',
+  '.mts': 'typescript',
   '.js': 'javascript',
   '.jsx': 'javascript',
   '.mjs': 'javascript',